Cellulose-coated radiative refrigeration wave absorber and method of making same

Abstract

The present application belongs to the cross technical field of electromagnetic wave absorbing material and radiation cooling material, and specifically provides a cellulose-coated radiation cooling wave absorber and a preparation method thereof, to solve the problem that the existing wave absorber is easy to absorb excessive solar radiation in an outdoor environment, causing device temperature rise and unstable operation. The present application uses PEDOT aerogel as the base body and introduces cellulose aerogel as the surface coating layer. On the one hand, high reflectivity is achieved in the visible light band to reduce solar radiation absorption, and on the other hand, high emissivity is achieved in the near-infrared band to release heat energy and suppress temperature rise, even achieving radiation cooling effect. At the same time, the cellulose aerogel is used as a perfect impedance matching layer to make the incident electromagnetic wave completely enter the material inside, improving the absorption efficiency. Furthermore, the PEDOT and cellulose are compounded to form an upper and lower structure network, so that the incident electromagnetic wave is reflected and scattered multiple times between the layers, prolonging the electromagnetic wave propagation path and further improving the absorption efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of electromagnetic absorbing materials and radiation cooling materials, specifically providing a cellulose-encapsulated radiation cooling absorber and its preparation method. Background Technology

[0002] Currently, with the rapid development of electronic information and wireless communication technologies and the continuous expansion of application scenarios, electromagnetic radiation sources are surging, and problems such as electromagnetic pollution, electromagnetic compatibility, and information protection are becoming increasingly prominent, urgently requiring high-performance electromagnetic absorbing materials. However, most existing electromagnetic absorbing materials are black and exhibit strong absorption characteristics in the visible and near-infrared regions. Consequently, in outdoor applications, they absorb excessive solar radiation, leading to localized temperature increases. This temperature rise not only compromises the operational stability of devices but also accelerates device aging and shortens their lifespan. Therefore, a novel absorbing material that combines efficient electromagnetic absorption with radiative cooling is urgently needed. Summary of the Invention

[0003] The purpose of this invention is to provide a cellulose-encapsulated radiation-cooled absorber and its preparation method, to solve the problem that existing absorbers easily absorb excessive solar radiation in outdoor environments, causing device temperature rise and operational instability. This invention uses PEDOT (poly-3,4-ethylenedioxythiophene) aerogel as a conductive matrix, utilizing its three-dimensional porous conductive network's dielectric loss characteristics to absorb electromagnetic waves. Simultaneously, a cellulose aerogel is introduced as an outer surface coating layer. The cellulose in this coating layer forms a dense porous structure and is rich in oxygen-containing functional groups such as hydroxyl and carboxyl groups. This achieves high reflectivity in the visible light band to reduce solar radiation absorption and high emissivity in the near-infrared band to release heat energy, suppress temperature rise, and even achieve a radiation-cooling effect. Furthermore, the cellulose aerogel has a low dielectric constant, serving as a perfect impedance matching layer, allowing incident electromagnetic waves to completely penetrate the material's interior, which is beneficial for improving the absorber's absorption efficiency. Moreover, the PEDOT and cellulose composite form an upper and lower structural network, causing multiple reflections and scattering of incident electromagnetic waves between layers, extending the electromagnetic wave propagation path and further improving absorption efficiency.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A cellulose-coated radiation-cooled absorber uses PEDOT aerogel as the matrix and cellulose aerogel as the surface coating layer, which is coated on the outer surface of the matrix. The dry weight ratio of PEDOT aerogel to cellulose aerogel is (1~5):1.

[0006] Furthermore, the average diameter of cellulose is 1 μm to 10 μm.

[0007] Furthermore, the preparation method of the above-mentioned cellulose-encapsulated radiation-cooled absorber includes the following steps:

[0008] Step 1. Mix the cellulose solution, deionized water, and trimethoxysilane in a certain proportion to form a cellulose dispersion;

[0009] Step 2. Add the cellulose dispersion to the PEDOT solution and mix thoroughly to form a matrix solution, with a dry weight ratio of cellulose to PEDOT of (0~1):1.

[0010] Step 3. Freeze the matrix solution at a low temperature to obtain the matrix;

[0011] Step 4. Place the matrix in a directional freeze-drying mold, add the cellulose dispersion to the mold at a dry weight ratio of PEDOT to cellulose of (1~5):1, freeze-dry at low temperature, and then freeze-dry to form an aerogel to obtain a cellulose-encapsulated radiation cooling absorber.

[0012] Furthermore, in step 1, the mass ratio of cellulose solution, deionized water and trimethoxysilane is 4:8:1, and the mass fraction of cellulose solution is 4%~5%.

[0013] Furthermore, in step 1, the mixing process is as follows: the mixed solution is placed in a homogenizer and stirred at a speed of 6000 rpm to 8000 rpm for 5 min to 10 min, and then ultrasonically treated at a power of 60W to 100W and a frequency of 34KHz to 41KHz for 10 min to 20 min.

[0014] Furthermore, the mass fraction of the PEDOT solution is 1.0% to 1.5%.

[0015] Furthermore, in step 2, the mixing process is as follows: the mixed solution is placed in a homogenizer and stirred at a speed of 6000 rpm to 8000 rpm for 5 min to 10 min, and then ultrasonically treated at a power of 60W to 100W and a frequency of 34KHz to 41KHz for 20 min to 30 min.

[0016] Furthermore, in step 3, the low-temperature environment is -20℃ to -176℃, and the freezing time is 5 min to 10 min.

[0017] Furthermore, in step 4, the low temperature environment is -80℃ to -176℃, the freezing time is 10min to 20min, and the freeze-drying time is 24h to 36h.

[0018] Furthermore, in step 4, the mold for directional freeze drying is composed of a metal base and a polytetrafluoroethylene layer thereon. Under low temperature conditions, cellulose can be oriented and grown, reducing porosity and increasing reflectivity under sunlight.

[0019] In terms of working principle:

[0020] This invention provides a cellulose-encapsulated radiation-cooled absorber, using PEDOT aerogel as the matrix and cellulose aerogel as the surface coating layer, covering the outer surface of the matrix. Cellulose aerogel exhibits high reflectivity in the visible light region and high emissivity in the near-infrared band, demonstrating excellent radiation-cooling properties. PEDOT aerogel, due to its high conductivity, exhibits good dielectric loss capability against electromagnetic waves. This invention introduces a cellulose coating layer into the structural design, causing the outermost layer to reflect a large amount of visible light to reduce heat absorption, and releasing heat energy through efficient near-infrared radiation to achieve cooling. The internal PEDOT matrix, under the influence of electromagnetic waves, causes electromagnetic waves to be reflected and scattered multiple times through the porous structure. Simultaneously, the cellulose aerogel, with its low dielectric properties, forms a perfect impedance matching layer, allowing incident electromagnetic waves to completely penetrate the material's interior, reducing surface reflection, and thus significantly improving absorption efficiency.

[0021] In summary, the beneficial effects of the present invention are as follows:

[0022] This invention employs a combination of solution casting and freeze-drying to prepare a radiation-cooled microwave absorber that encapsulates PEDOT aerogel with cellulose aerogel. Utilizing the dense structure and oxygen-containing functional groups on the surface of cellulose, high reflectivity is achieved under visible light, and high emissivity is achieved in the near-infrared band, thus enabling the absorber to exhibit a significant radiation-cooling effect. Simultaneously, the three-dimensional conductive network of PEDOT aerogel effectively reflects and scatters incident electromagnetic waves, extending the electromagnetic wave propagation path. Furthermore, the cellulose aerogel acts as a perfect impedance layer, introducing incident electromagnetic waves into the material's interior, reducing surface reflectivity, and achieving highly efficient broadband absorption performance. Attached Figure Description

[0023] Figure 1 This is a physical image of the cellulose-encapsulated radiation-cooled absorber in an embodiment of the present invention.

[0024] Figure 2 The image shows the morphology of the cellulose aerogel encapsulated in the cellulose radiation-cooling absorber in this embodiment of the invention under a scanning electron microscope.

[0025] Figure 3 The image shows the reflection spectrum of the cellulose-encapsulated radiation-cooled absorber in the visible light band in an embodiment of the present invention.

[0026] Figure 4The emissivity spectrum of the cellulose-encapsulated radiation-cooled absorber in the near-infrared band is shown in an embodiment of the present invention.

[0027] Figure 5 This is an outdoor radiative cooling effect diagram of the cellulose-wrapped radiative cooling absorber in an embodiment of the present invention.

[0028] Figure 6 This is a diagram showing the terahertz absorption performance of the cellulose-coated radiation-cooled absorber in an embodiment of the present invention.

[0029] Figure 7 This is a diagram showing the microwave absorption performance of the cellulose-coated radiation-cooled absorber in an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] This embodiment provides a cellulose-encapsulated radiation-cooled absorber and its preparation method. The radiation-cooled absorber uses PEDOT aerogel as a matrix and cellulose aerogel as a surface coating layer, which is coated on the outer surface of the matrix. It is prepared by the following steps:

[0032] Step 1. Using a dropper, take 20g of cellulose solution (the cellulose mass fraction in the cellulose solution is 4.5 wt%, and the calculated cellulose content is 0.9g), 40g of deionized water, and 5g of trimethoxysilane solution. Mix the three solutions and place them in a homogenizer. Stir at 6000 rpm for 5 minutes, and then sonicate at 100 W and 40 kHz for 10 minutes to form a cellulose dispersion (at this point, the cellulose mass fraction in the dispersion is approximately 1.385 wt%).

[0033] Step 2. Take 1g of the above cellulose dispersion and 50g of PEDOT solution (PEDOT mass fraction is 1.3wt%, calculated to be approximately 0.65g of PEDOT), and place them in a clean beaker; after mixing, place them in a homogenizer and stir at 6000 rpm for 10min, and then sonicate at 100 W power and 40 kHz frequency for 20min to obtain the matrix solution;

[0034] Step 3. Freeze the obtained collective solution at a low temperature (-176℃) for 5~10 minutes to solidify;

[0035] Step 4. Place the PEDOT matrix in a directional freeze-drying mold. Use a dropper to take 38g of cellulose dispersion (containing approximately 0.526g of cellulose) and pour it into the mold to coat the matrix. At this point, the dry weight ratio of PEDOT in the matrix to cellulose in the coating layer is 1.23:1. Freeze the resulting liquid at a low temperature (-176℃) for 20 minutes to form the matrix; then freeze-dry for 36 hours to obtain a radiation-cooled microwave absorber with cellulose-coated PEDOT aerogel.

[0036] like Figure 1 The image shown is a physical picture of the cellulose-encapsulated radiation cooling absorber obtained in this embodiment. The left image is the front view, and the right image is the back view. As can be seen from the image, the cellulose aerogel (white) serves as the surface coating layer, covering the outer surface of the PEDOT aerogel (black) (excluding the bottom). It should be noted that, with the help of other molds, the cellulose aerogel (white) can also form a complete coating on the PEDOT aerogel (black).

[0037] like Figure 2 The image shows the morphology of the cellulose-encapsulated radiation-cooling absorber in this embodiment under a scanning electron microscope. As can be seen from the image, the cellulose pores are uniform in size and grow with a certain orientation.

[0038] like Figure 3 The figure shows the visible light reflectance spectrum of the cellulose-coated radiation-cooled absorber in this embodiment. As can be seen from the figure, the average reflectance of the absorber in the visible light band is greater than 95%.

[0039] like Figure 4 The figure shows the emissivity spectrum of the cellulose-coated radiation-cooled absorber in this embodiment under near-infrared light. As can be seen from the figure, the average emissivity of the absorber in the range of 8-13 μm exceeds 96%.

[0040] like Figure 5 The figure shows the outdoor radiative cooling effect of the cellulose-coated radiative cooling absorber in this embodiment. As can be seen from the figure, the outdoor test shows that the absorber is significantly cooler than the ambient temperature, demonstrating a good radiative cooling effect.

[0041] like Figure 6 and Figure 7 The figure shows the electromagnetic wave absorption performance of the radiation-cooled absorber encapsulated in PEDOT aerogel and cellulose in an embodiment of the present invention. The absorption performance of the absorber in the range of 0.5THz to 4THz and 40GHz to 67GHz was measured using a terahertz time-domain spectroscopy system and a vector network analyzer. The results are as follows. Figure 6 and Figure 7As shown in the figure, both the cellulose-coated radiation-cooled absorber and the PEDOT aerogel exhibit absorption rates of over 99.9% in the range of 0.5THz to 3.5THz and over 90% in the range of 50GHz to 67GHz, demonstrating broadband and efficient absorption performance. Furthermore, the cellulose-coated radiation-cooled absorber, with its low dielectric properties, reduces surface reflection and significantly improves the absorption performance of the absorber.

[0042] In summary, this invention achieves multiple functions of visible light reflection, near-infrared emission, and electromagnetic wave absorption through the synergistic design of cellulose outer coating and PEDOT matrix, effectively solving the problem of excessive temperature rise caused by heat absorption in traditional absorbers in outdoor environments.

[0043] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A cellulose-coated radiation-cooled absorber, characterized in that, The radiation-cooled absorber uses PEDOT aerogel as the matrix and cellulose aerogel as the surface coating layer, which is coated on the outer surface of the matrix. The dry weight ratio of PEDOT aerogel to cellulose aerogel is (1~5):

1.

2. The cellulose-coated radiation-cooled absorber according to claim 1, characterized in that, The average diameter of cellulose is 1 μm to 10 μm.

3. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 1, characterized in that, Includes the following steps: Step 1. Mix the cellulose solution, deionized water, and trimethoxysilane in a certain proportion to form a cellulose dispersion; Step 2. Add the cellulose dispersion to the PEDOT solution and mix thoroughly to form a matrix solution, with a dry weight ratio of cellulose to PEDOT of (0~1):

1. Step 3. Freeze the matrix solution at a low temperature to obtain the matrix; Step 4. Place the matrix in a directional freeze-drying mold, add the cellulose dispersion to the mold according to the dry weight ratio of PEDOT to cellulose of (1~5):1, freeze-dry at low temperature, and then freeze-dry to form an aerogel to obtain a cellulose-encapsulated radiation cooling absorber.

4. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 1, the mass ratio of cellulose solution, deionized water and trimethoxysilane is 4:8:1, and the mass fraction of cellulose solution is 4%~5%.

5. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 1, the mixing process is as follows: the mixed solution is placed in a homogenizer and stirred at a speed of 6000 rpm to 8000 rpm for 5 min to 10 min, and then ultrasonically treated at a power of 60W to 100W and a frequency of 34KHz to 41KHz for 10 min to 20 min.

6. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 2, the mixing process is as follows: the mixed solution is placed in a homogenizer and stirred at a speed of 6000 rpm to 8000 rpm for 5 min to 10 min, and then ultrasonically treated at a power of 60W to 100W and a frequency of 34KHz to 41KHz for 20 min to 30 min.

7. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 3, the low temperature environment is -20℃ to -176℃, and the freezing time is 5 min to 10 min.

8. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 4, the low temperature environment is -80℃ to -176℃, the freezing time is 10 min to 20 min, and the freeze-drying time is 24 h to 36 h.

9. The method for preparing the cellulose-encapsulated radiation-cooled absorber according to claim 3, characterized in that, In step 4, the mold for directional freeze drying consists of a metal base and a polytetrafluoroethylene layer thereon.

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